Encoder system using linear array sensor for high resolution

Abstract

An encoder system and method wherein an encoder element driven by a motor has a series of segments arranged along a path with adjacent segments having different properties meeting at an edge or transition, two adjacent segments of different properties comprising a cycle and the encoder element having a number of cycles equally spaced along the path and defining a relatively coarse pitch relationship. A coupling medium, preferably optical, images the encoder segments onto a number of individual sensor elements of an array, such as a charge-coupled device sensor, wherein the sensor elements are spaced at a relatively fine pitch along the array. As the encoder element is moved by the motor, images of the edges or transitions are applied to the array sensor elements After a sampling interval, signals from the array are digitized and shifted into a microprocessor which compares the present locations of the applied edges to the previous locations stored in the memory thereof and which calculates the present position and velocity output signals which can be used to control operation of the motor in a closed loop feedback control system. The encoder system achieves high resolution with a relatively coarse pitch and thus low cost encoder element. In addition, both position and velocity signals are derived from operation of the single encoder element.